1. Field of the Invention
The present invention relates to a motor driven fuel pump for supplying liquid fuel from a tank to a fuel injection system of an automotive engine.
2. Description of the Prior Art
Displacement type pumps utilizing roller pumps have generally been used for the purpose specified above, as disclosed in U.S. Pat. No. 4,181,473, for example. Roller pumps, however, have difficulties that rollers are driven in sliding contact with the inner surfaces of pump chambers and that high levels of noises are produced due to pulsations of discharge pressures. This latter difficulty is not compatible with recent motor vehicles which are required to be operated as quietly as possible. In addition, motor pumps disadvantageously utilize a large number of component parts.
In order to eliminate the difficulties and disadvantage, it has been proposed to form a fuel pump by a regenerative pump (which is also called as "peripheral pump" or "Wesco pump"), as disclosed in U.S. Pat. No. 3,259,072. The pump of this type is not of the displacement type but produces a discharge pressure which is generally satisfactory to fuel injection systems of internal combustion engines. The regenerative or peripheral pump, however, has a shortcoming that the housing defining therein an impeller or pump chamber needs a relatively large amount of material such as a plastics material, as will be seen in FIG. 3 of the U.S. patent referred to. Thus, there has been a demand for a motor driven regenerative pump which is of a reduced size and provides an increased pump efficiency. Moreover, with the structure and arrangement of the regenerative pump shown in FIG. 3 of the U.S. patent referred to, the liquid fuel pressurized in the fuel pressurizing passage or "ring channel" 40 impinges upon the "sealing body" 46 at the discharge end of the "ring channel" 40, so that the dynamic pressure rises at the discharge end of the "ring channel". This disadvantageously increases the leakage of fuel through the inner surface of the "sealing body" 46 and the outer periphery of the impeller 36.